1. Field of the Invention
The present invention relates to a liquid crystal display capable of color display for use in a display section of an information appliance and others.
2. Description of the Related Art
A liquid crystal display is provided with a pair of substrates each having a transparent electrode on the sides facing each other, and a liquid crystal layer sealed between these substrates. Through voltage applied between the transparent electrodes, the liquid crystal display drives the liquid crystal to control the light transmissivity of the liquid crystal on a pixel basis. In recent years, the liquid crystal display is used as a display section for a notebook PC, a television receiver, a display monitor, a PDA (Personal Digital Assistant), a projection projector, and others. The demand for the liquid crystal display has been increasing, accompanied with higher expectations therefor. Especially, improvement of the display quality is demanded.
For improvement of the display quality, chromaticity adjustment is a possible method. The liquid crystal display of a general type capable of color display optimizes the chromaticity during display of white (whiteness). Such optimization is done through adjustment of spectrum distribution of light beams emitted from a light source such as a backlight unit, or through adjustment of chromatic balance of color filters (CF) provided for pixels of red (R), green (G) and blue (B).
The issue here is that even if whiteness is optimized though such adjustment, it does not necessarily optimize chromaticity during display of black (blackness). It is often considered desirable if black chromaticity matches white chromaticity. However, merely adjusting whiteness does not achieve such match between blackness and whiteness, causing color level difference (chromatic deviation). An adjustment optimizing blackness while keeping whiteness at its optimum level is extremely difficult.
If there is any color level difference, a color-tint phenomenon occurs during display of black. The causes for such a color-tint phenomenon are varying in type, e.g., spectrum distribution of illumination light, dependence of retardation of the liquid crystal layer on wavelength, color level balance of color filters provided for every color pixel, material contrast value expressing the depolarization property of the colored resin (color resist) forming the color filter and structural property of polarization plates and panels.
For example, if any slight light leakage is found during display of black due to the dependence of retardation of the liquid crystal layer on wavelength, a color-tint phenomenon occurs by reason of color level difference. That is, if blackness shows a bias toward blue with respect to whiteness, black display is tinted blue. If this is the case, an exemplary solution may be the multigap structure in which the cell gap thickness of a blue pixel region is made different from the cell gap thickness of red and green pixel regions to reduce the color-tint level to some degree. The problem of such a multigap structure is that if blackness shows a bias toward green or red with respect to whiteness, the color tint cannot be reduced sufficiently.
Moreover, even if any desired whiteness is derived through adjustment of the color level balance of the color filters provided for every color pixel, and even if the color resists are provided with the same material contrast value, the color level during display of black may not be the desired level due to color-tinting caused by the polarization plate, color-tinting caused by the liquid crystal molecule alignment, or other reasons. What is worse, depending on the panel structure, some specific color pixel region may suffer from liquid crystal molecule misalignment. As a result, in such a color pixel region, the transmissivity is increased during display of black, thereby causing color-tint.
As such, the larger color level difference causes color-tint during display of black, and this is a cause of considerably lowering the display quality as the liquid crystal display.
[Patent Document 1] JP-A-9-005736